1. Field of the Invention
The invention relates to the field of planet orbiting satellites and, in particular, to combined solar array and antenna assembly for a satellite wherein thermal balance is maintained between the two.
2. Description of Related Art
Thermal management of satellite systems is complex, costly, and difficult to achieve. There are tremendous heat dissipation requirements, typically in the 10 kW to 15 kW range. High component density, large surface areas, and the low volume available for thermal control systems aggravate this. For example, a typical satellite may have a 400 to 600 square foot planar array antenna payload and single or two axes tracking solar arrays. In this configuration, a spacecraft moves through various beta angles (the angle of the sun to the orbital plane), spacecraft re-orientations are required to maintain solar array tracking. This configuration also requires at least two separate deployment sequences, one for the solar array assembly and one for the planar array antenna. Of course, deployment mechanisms and latches that are separately required for the solar array assembly and planar array antenna.
The driving thermal factor of the planar array antenna is the enormous size, combined with the thermal optical properties on the radiating surface of the planar array antenna. These characteristics create a large thermal radiator that is extremely sensitive to the thermal environment. While this is advantageous when dissipating several kilowatts of heat, it becomes a great disadvantage during non-operating or short operating periods. During operational scenarios, planar array antennas are frequently designed to rotate about a single or dual axis off from nadir (earth pointing orientation) to acquire their targets. These rotations from nadir subject the antenna to extreme thermal environments that can be either hot (toward the sun) or cold (away from the sun).
A. If the target location results in the planar array antenna rotating toward the sun, the thermal control system must be able to handle extremely hot environments, several kilowatts of heat dissipation and not exceed its"" hot temperature limits.
B. If the target location requires the planar array antenna to rotate toward deep space and the operational duty cycle is low; the thermal control system must be able to handle very cold environments. Several kilowatts of peak heater power can be required to maintain planar array antenna temperatures.
C. In both the hot and cold scenarios, as the planar array antenna rotates away from the nadir, operation times can be severely limited without complicated controls. Typically, rotations beyond a 30-degree rotation from nadir results in shortened operate times and higher heater power requirements.
In addition, during all non-operating modes, it is desirable for the planar array antenna to be nadir pointing to reduce the amount of heater power required. In a xe2x80x9csafe modexe2x80x9d and through deployment sequences, it may be difficult to maintain the solar array assembly toward the sun and planar array antenna towards the earth. As a result, several kilowatts of heater power can be required to maintain the planar array antenna within temperature limits.
The lack of xe2x80x9creal estatexe2x80x9d due to the high density of components makes the installation of heaters difficult. As a result heaters are often applied in non-optimum locations and must depend upon radiation to the local environment, which then provides uniform heating to the planar array antenna. Finally a nadir pointing planar array antenna generally also requires a radome to act as a radiation barrier to the environment.
There have been attempts to combine antenna and solar array collectors. For example, U.S. Pat. No. 4,864,317 xe2x80x9cCombination Satellite Antenna-Solar Collectorxe2x80x9d by P. O. Sorko-Ram. Here the same reflector dish used for satellite communications is coupled to a heat exchanger system. Thus when not operating as an antenna, it can be used to collect solar energy. However, it can not be used in orbit where a solar array must operate simultaneously with the antenna. Also of interest is U.S. Pat. No. 3,594,803 xe2x80x9cIntegrated Thermoelectric/Generator/Space Antenna Combinationxe2x80x9d by G. L. Pucillo, et al. The invention is an antenna formed of hot and cold themoelectric element. Thus power can be generated as the antenna transmits to a satellite. Here again, no attempt is made to control the temperature of the antenna.
Thus it is a primary object of the invention to provide a combination solar panel and planar array antenna that eliminates the need for complex thermal control systems.
It is another primary object of the invention to provide a combination solar panel and planar array antenna that uses passive heat exchange techniques control the temperature of each.
It is a further object of the invention to provide a combination solar panel and planar array antenna that eliminates the need for complex thermal control systems that does not require a radome for the planar antenna.
The invention is a combination solar panel and planar array antenna for a satellite. In detail, the invention includes a generally flat solar array assembly having first (external) and second (internal) surfaces, the first surface having solar energy collecting devices thereon. A generally flat planar array antenna having first (external) and second (internal) surfaces is coupled to the flat solar panel, with the first surface for receiving and transmitting electromagnetic energy. The planar array antenna is coupled to the solar panel assembly such that the internal surfaces of the solar array assembly and the planar array antenna face each other. The internal surfaces of the solar array assembly and the planar array antenna have high emissive thermal coatings. The external surface of the planar array assembly has an absorptive/high emissive thermal coating.
The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which the presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention.